Let Gamma be a Bieberbach group - that is a torsion free crystallograp
hic group. In this paper we give a list of the isomorphism types of al
l holonomy groups of five-dimensional Bieberbach groups. An applicatio
n to the problem of estimating the covolume of a discrete group of ori
entation-preserving isometries of hyperbolic 6-space is also given.